Jeep Liberty Runs overheated / Runs Hot

#1

Hopped on the freeway today for a 10 hour drive home from my parents house. About an hour out of town my car suddenly overheated. My Dad drove up and we removed the thermostat. The car at that point didn’t overheat but it ran between 5/8ths and 7/8ths up the temperature scale as I worked my down the freeway back home (the redline starts at about 7/8ths up the scale). When I coasted on long downhill stretches as well as driving slowly through town the temperture dropped to normal range (needle more or less straight up). Once in town I bought a new thermostat and installed it and still have the same symptoms as when the thermostat was out, i.e. when driving 50mph or above the temperture stays right below red but when I drive under 50 it runs around normal. The thought is we will remove the water pump tomorrow to check if it isn’t working (water pump isn’t making any “howling” sounds, which my Haynes manual says suggests means bad shaft bearings).

My question is, what else, besides the water pump could be causing the engine to run hot yet not overheat when under load (driving uphill or accelerating on level roads) and running at normal temp when driving in town, or downhill, or maintaining level speed on flat grades?

Additional observations: The heater, when the thermostat was removed, blew out air the temperature of the outside air. Since replacing the thermostat the heater will alternate between blowing hot air and outside temperature air. I’m not sure that I added water back to the system the correct way. The Haynes manual says to simply refill the expansion tank, run the engine until normal operating temp is reached and then adding additional water as necessary. We think that there may be some other method required in order to properly fill the radiator and eliminate any air pockets. We’ve tried several ways but can’t figure out any other way that makes a difference. Also, I should note that there don’t appear to be any leaks…the 1 hour drive back home and the coolant was still full and we couldn’t find any leaks.

If I think of any other information I’ll try to add it, or if anybody has any questions I’ll try to answer them the best I can. Thank you!

-Nick

#2

Also, just thought about it, we eliminated blow head gasket as there is no moisture coming out of the tailpipe, and no coolant in the oil.